1. Field of the Invention
This invention relates to a surface-decorated article having on its surface a golden or silvery noble metal decorating matter which is not damaged on being exposed to high-frequency electro-magnetic waves radiated by an electronic range, and a method for preparing the surface-decorated article. The invention also relates to a liquid gold for overglaze decoration employed therefor.
2. Related Art
In the following, discussions on the related art will be first presented briefly.
Among ceramic articles, such as porcelain, china wares, earthen wares or pottery (termed herein commulatively as "ceramic wares"); glass ware or enamel ware, there are such articles having beautiful golden or silvery decorative matter on its surface for giving elegant or gorgeous impression.
The conventional surface-decorated articles by noble metal are prepared by coating liquid gold containing organic compounds of noble metal represented by gold resin balsam sulfide on the article surface by brushing, straying or with the aid of printing paper etc. and subsequently baking the article for adhesion.
However, when the surface-decorated articles thus produced are heated by an electronic range, sparks are generated on the surface of the noble metal decorating matter thus possibly damaging the decorating matter by cracking or peeling off.
This is ascribable to the fact that the nobel metal compound of the noble metal decorating matter is electrically conductive.
Thus, investigations in electrically non-conductive noble metal decorating matter, not producing damages during use in the electronic range, are recently under progress.
For example, in JP Patent kokai Publications JP-A-55-51776 (1980) and JP-A-55-56079 (1980), frits free of lead or containing only a minor quantity of lead are contained along with the golden components. It is stated therein that the respective noble metal particles are sheathed by frits contained in the composition and attain a vitrified state by fusion of the frits brought about by firing thus assuring superior abrasion resistance and resistance against chemicals, in addition to resistance against electricity.
On the other hand, there is disclosed in JP Patent Kokoku Publications JP-B-2-36558 (1990) and JP-B-5-13113 (1993) a liquid gold or paste gold for overglaze decoration, containing organic compounds of bismuth, indium and silicon. It is stated therein that the noble metal decorating matter, that is gold alloy, prepared by employing the noble metal for overglaze decoration, becomes electrically non-conductive by the above composition.
In addition, in JP Patent Kokai Publication JP-A-6-48779 (1994), there is contained barium in addition to the above-mentioned components of rendering the gold alloy electrically non-conductive for improving gold or silver color-developing characteristics.
However, the above-described conventional ceramic articles, such as ceramic wares, glassware or enamelware, having coated thereon a golden or silvery noble metal decorating matter for use on an electronic range, are rendered insulating by adding insulating inorganic components in the noble metal for overglaze decoration in the form of organic compounds or frits for prohibiting sparking even when the articles are employed in the electronic range.